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A novel folded shorted patch antenna for broadband operation is presented. It has an impedance bandwidth (SWR <2) of 99.4%, which is more than three times that of the antenna without slots. Also, it is (1.085λ^sub L^ in height and (1.14λ^sub L^ in length, where λ^sub L^ is the free space wavelength at the lower cutoff frequency of its operating bandwidth. Therefore, it is very suitable for today's multiband indoor wireless communication systems.
Introduction: The micro strip patch antenna has the attractive characteristics of low profile, light weight and simple structure. However, its bandwidth is limited to a few percent, which is not enough for most modem wireless communication systems. In fact, one of the popular bandwidth enhancement techniques is to etch a U-slot on the patch and use a thick foam substrate [ 1 ]. This can increase the bandwidth of a conventional patch antenna to around 40%. If an additional U-slot is cut on the patch, bandwidth of up to 44% can be obtained [2], Nevertheless, these antennas have the same disadvantage of large lateral size. Indeed, researchers have proposed several methods to tackle this problem. They include the use of shorted wall [3], shorted pins [4], half U-slot patch [5] and a combination of all these [6], Unfortunately, these methods will reduce the bandwidth of a U-slot patch antenna to 14.6-28%.
Other than the U-slot patch, the stacked patch is also a common technique to enhance the bandwidth of a conventional patch antenna. By placing an additional patch above the original one, a bandwidth of 10-20% can be achieved [7], To minimise the antenna size, both patches are shorted to the ground plane by a common metallic wall [8], Although this E-shaped patch antenna has wider bandwidth of 30% and smaller size, it is difficult to construct since soldering is required between the lower and the upper patches. Recently, a novel stacked shorted patch antenna was proposed. It is developed by moving the shorted wall between the lower patch and the ground plane of the E-shaped patch antenna to the opposite edge of the lower patch [9], This folded shorted (or S-shaped) patch antenna not only has a simple structure, but also has a wide...